This invention relates to a lighting device for an observation unit, an image pickup unit or the like which is used for observing or picking up an image of a surface of a specimen sample, and more particularly to an improvement in a lighting device which is adapted to light or illuminate a surface of a section to be observed (hereinafter referred to as "observed section") of a specimen sample while providing a light field due to vertical projection and/or a dark field due to lateral projection as required.
There are conventionally known an observation unit for observing an image or magnified image of a surface of an observed section of a specimen sample which is an object subject to observation and an image pickup unit for displaying the image on a picture plane of a monitor TV to indirectly observe it. Each of the observation unit and the image pickup unit is adapted to locate a lighting head or an image pickup head each having a projecting means incorporated therein in a manner to face the surface of the observed section of the specimen sample to light the observed section, to thereby permit the observation to be carried out. In each of the observation unit and image pickup unit thus constructed, lighting is generally carried out by a vertical projection method mainly using vertically projected light wherein parallel light beams are vertically irradiated to a longitudinal surface portion of the surface of the observed section of the specimen sample in a direction perpendicular thereto or by a lateral projection method mainly using laterally projected light wherein light beams are obliquely irradiated to the longitudinal surface portion of the surface of the observed section a direction oblique with respect to the surface portion.
However, when the surface of the specimen sample which is an object subject to observation has relatively fine unevenness, individual execution of the vertical projection method or lateral projection method fails to permit the fine unevenness on the surface to be precisely observed. In order to avoid the problem, concurrent execution of both projection methods would be considered. Unfortunately, this causes the observation device or image pickup device to be highly complicated in structure.